Predicting Steady Shear Rheology of Condensed-Phase Monomolecular Films at the Air-Water Interface (original) (raw)
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Transition from Newtonian to non-Newtonian surface shear viscosity of phospholipid monolayers
Physics of Fluids, 2013
The surface shear viscosity of DPPC (dipalmitoylphosphatidylcholine) monolayers on the air/water interface was determined over a wide range of surface concentrations in an annular channel. DPPC is studied widely because it is ubiquitous in biological systems. Brewster angle microscopy (BAM) was found to be capable of measuring the monolayer velocity field, even in the absence of co-existing phase domains. Interfacial velocimetry via cross correlations of BAM images provides accurate and non-invasive measurements, useful for both macro and microrheology. The measured velocity profiles are compared with computed profiles obtained over a range of surface shear conditions using the Boussinesq-Scriven surface model, from which the surface shear viscosity was determined. For monolayers in the liquid expanded (LE) and liquid expanded/liquid condensed (LE/LC) co-existing phases, we observe Newtonian behavior. We also show how the flow departs from the Newtonian regime for monolayers with larger surface concentration, corresponding to LC phase transition to solid phase.
Langmuir, 2010
Many biologically relevant monolayers show coexistence of discrete domains of a long-range ordered condensed phase dispersed in a continuous, disordered, liquid-expanded phase. In this work, we determined the viscous and elastic components of the compressibility modulus and the shear viscosity of monolayers exhibiting phase coexistence with the aim at elucidating the contribution of each phase to the observed monolayer mechanical properties. To this purpose, mixed monolayers with different proportions of distearoylphosphatidylcholine (DSPC) and dimyristoylphosphatidylcholine (DMPC) were prepared and their rheological properties were analyzed. The relationship between the phase diagram of the mixture at 10 mN m -1 and the rheological properties was studied. We found that the monolayer shear viscosity is highly dependent on the presence of domains and on the domain density. In turn, the monolayer compressibility is only influenced by the presence of domains for high domain densities. For monolayers that look homogeneous on the micrometer scale (DSPC amount lower that 23 mol %), all the analyzed rheological properties remain similar to those observed for pure DMPC monolayers, indicating that in this proportion range the DSPC molecules contribute as DMPC to the surface rheology in spite of having hydrocarbon chains four carbons longer.
Shear rheology of lipid monolayers and insights on membrane fluidity
Proceedings of the National Academy of Sciences, 2011
The concept of membrane fluidity usually refers to a high molecular mobility inside the lipid bilayer which enables lateral diffusion of embedded proteins. Fluids have the ability to flow under an applied shear stress whereas solids resist shear deformations. Biological membranes require both properties for their function: high lateral fluidity and structural rigidity. Consequently, an adequate account must include, in addition to viscosity, the possibility for a nonzero shear modulus. This knowledge is still lacking as measurements of membrane shear properties have remained incomplete so far. In the present contribution we report a surface shear rheology study of different lipid monolayers that model distinct biologically relevant situations. The results evidence a large variety of mechanical behavior under lateral shear flow.
Oscillatory shear rheology measurements and Newtonian modeling of insoluble monolayers
Physical Review Fluids, 2017
Circular systems are advantageous for interfacial studies since they do not suffer from end effects, but their hydrodynamics is more complicated because their flows are not uni-directional. Here, we analyze the shear rheology of a harmonically-driven knife-edge viscometer through experiments and computations based on the Navier-Stokes equations with a Newtonian interface. The measured distribution of phase lag in the surface velocity relative to the knife-edge speed is found to have a good signal-to-noise ratio and provides robust comparisons to the computations. For monomolecular films of stearic acid, the surface shear viscosity deduced from the model was found to be the same whether the film is driven steady or oscillatory, for an order of magnitude range in driving frequencies and amplitudes. Results show that increasing either the amplitude or forcing frequency steepens the phase lag next to the knife edge. In all cases, the phase lag is linearly proportional to the radial distance from the knife edge and scales with surface shear viscosity to the power −1/2.
Surface viscoelasticity of phospholipid monolayers at the air/water interface
Colloid & Polymer Science, 1996
The surface viscoelastic properties of monolayers of two phospholipids DPPC (L-cc-dipalmitoylphosphatidylcholine) and DMPE (L-c~-dimyristoylphosphatidylethanolamin), at the air-water interface have been investigated. Two techniques were used for the investigation. One involved use of an interracial shear rheometer (torsion pendulum apparatus ISR1), to provide measurements of the shear viscosity t/s as a function of surface pressure, and the second, a modified LB trough with an oscillating barrier to generate periodic dilation and compression so as to measure the dilational elastic modulus E as a function of surface area.
Langmuir, 1999
Poly(ethylene glycol) (PEG) is a molecule that exhibits unique behavior when compared with polymers in its homologous family. Depending on its environment, it may show hydrophilic, hydrophobic, or amphiphilic properties. We have studied several PEG lipopolymers, where a PEG chain with a molecular weight (MW) of 2000 g/mol or 5000 g/mol is covalently attached to 1,2-dipalmitoyl-or 1,2-distearoyl-sn-glycero-3phosphoethanolamine, with a Langmuir film balance and a recently developed interfacial stress rheometer. In particular, we have determined how the rheological properties of PEG molecules anchored at the airwater interface change when the polymer chains are forced into highly stretched brush conformations. Pressure-area isotherms of monolayers of PEG lipopolymers exhibit two phase transitions: a desorption transition of the PEG chains from the air-water interface at 10 mN/m and a high film pressure transition at 20-40 mN/m, but the nature of the latter transition is still poorly understood. We have observed a remarkable change of the viscoelastic properties in the range of the high-pressure transition. The monolayer is fluid below the transition, with the surface loss modulus, Gs′′, being larger than the surface storage modulus, Gs′, but becomes remarkably elastic above, with Gs′ > Gs′′. This indicates that a strong correlation exists between the reversible, first order-like high-pressure transition and the formation of a physical gel. Our surface rheological experiments indicate that formation of a physical network can be understood if water intercalates mediate the interaction between adjacent PEG chains via hydrogen bonding.
Coupling between protein-laden films and a shearing bulk flow
Journal of Colloid and Interface Science, 2008
Two-dimensional protein crystallization on lipid monolayers at a quiescent air/water interface is now a well-established process, but it only operates under a very restricted set of conditions and on a very slow time scale. We have recently been able to significantly extend the conditions under which the proteins will crystallize as well as speed up the process by subjecting the interface to a shearing flow. Here, we investigate the two-way coupling between a protein-laden film and the bulk flow that provides the interfacial shear. This flow in a stationary open cylinder is driven by the constant rotation of the floor. Using the Boussinesq-Scriven surface model for a Newtonian interface coupled to the Navier-Stokes equations for the bulk flow, we find that the surface shear viscosity of protein-laden films under most conditions is small or negligible. This is the case for films subjected to constant shearing flow, regardless of the duration of the flow. However, when the film is intermittently sheared, significant surface shear viscosity is evident. In these cases, the surface shear viscosity is not uniform across the film.
Biophysical Chemistry, 2003
There is lack of thermodynamic studies to describe the LE-LC 2D-phase transition of dipalmitoyl phosphatidyl glycerol (DPPG) although it is one of the main components of lung surfactants. Spread monolayers of synthetic DPPG are investigated in a broad temperature range on subphases modeling the native biological substrate. The phase transition pressure changes linearly with temperature, which confirms the principal applicability of the two-dimensional Clausius-Clapeyron equation to evaluate thermodynamic data of such systems. Brewster angle microscopy performed at monolayer compression shows that it is strongly heterogeneous during phase transition. The competition between strong condensation effects of Ca 2+ cations on the negatively charged DPPG anions and electrostatic repulsion due to Na + ions preventing condensation leads to a very fast growth of the LC phase. As a consequence, strong irregularities in the domain shapes and size distribution are observed. A new approach is proposed to determine the molar area at the phase transition from the set of π/A isotherms recorded at different temperatures. The two-dimensional Maxwell relation and Clausius-Clapeyron equation were simultaneously applied to calculate the required parameters with a reasonable accuracy. The entropy changes at the phase transition, transition heats, and the critical temperature are calculated.
Surface rheology of monolayers
Thin Solid Films, 1996
The surface rheological behaviour of spread monolayers of DPPC (L-cY-dipalmitoyl phosphatidyl chinoline) and DMPE (L-a-dimyristoyl phosphatidyl ethanolamine) on water has been investigated under shear and dilation/compression deformation. Harmonic area perturbations are performed using an oscillating barrier method which provides information on the monolayer dilational elasticity and the relaxation processes happening in the monolayers as a function of surface pressure. A surface shear rheometer has been used to measure the surface shear viscosity and elasticity of the same monolayers. The shear and dilational rheological properties can be explained by the morphology of the phospholipid monolayers as a function of surface pressure.
Shear viscosity of polymer and surfactant monolayers
The European Physical Journal E, 2000
The surface shear viscosity of monolayers formed at the surface of water by adsorbed polyethyleneoxyde and by stearic acid is measured as a function of the surface pressure of the monolayer using a new surface viscometer. The principle of the viscometer is the measurement of the drag force on a circular disk undergoing a uniform translation at the water surface: a hydrodynamic model based on the lubrication approximation allows a calculation of the surface viscosities from the absolute measurement of the drag forces.